(1)
Faculty of Medicine of Montpellier, Montpellier, France
Abstract
The reproductive function is mandatory for species survival. This requires, to be efficient, an intelligent automation of the processes and a real motivation of the partners which is based on an important parameter: the pleasure, which is one of the main motor of reproduction. In order to make possible the union of two gametes (spermatozoon and ovule) within the genital tract of the female to create a new individual, it is needed to have some specific anatomical features: a variable stiffness penile injector, a bulbospongiosus urethral pump made by striated perineal muscles and an orgasmic ejaculation seizure generating expulsion of sperm and pleasure. This is provided by the firing of neurons of the ejaculation spinal centre in men, and the same orgasmic seizure can be recorded in women after appropriate stimulation of the clitoridian inductor. Most of the sexual problems are linked to a lack of knowledge of these neurophysiological precise processes.
10.1 Introduction
The reproductive function is essential for the maintenance of species by organising the union of male and female gametes to produce a new individual. It is also under the control of striated muscle functions that need a particular technical programme.
This “survival kit” represents the mechanisms of species survival, all of whom, except man, do not know the biology and are totally ignorant. That is why automation is an absolute necessity as well as a rigorous programming of the three survival processes: search for food [1] (individual survival), search for partner for reproduction (species survival) and marking a territory where to find food and partners.
These three aspects are dependent on the limbic system [2], which is a generator of survival behaviours, placed in the brain of all species including humans.
Some animals have only a limbic cortex and spend all their time eating, copulating and defending their territory. Man has an extensive surrounding limbic system with cingulate gyrus, hippocampus, fornix, thalamus, amygdala, septal area, hypothalamus, raphe nuclei but also a supralimbic cortex allowing him to control more or less well limbic impulses. For example, the typically limbic territoriality typically can be very active in explaining human wars, crimes and jealousy in all its forms expressed in human couples, families and even in occupations, including universities.
This chapter is devoted to reproduction [3], a part of the limbic survival kit programme that requires examining a number of related technical problems answering the question: how to reproduce?
10.2 Technical Problems of Copulation
The objective is to put together in a receiving cavity two gametes, male and female, which are nanotechnological components. The spermatozoon has a head of 5 μm in length for a total length of 60 μm. The ovule has a diameter of 200 μm. Their union allows first fertilisation and the gradual development of an embryo, then a foetus and finally a newborn. Therefore several technical features are necessary to achieve this programme.
10.2.1 Variable Stiffness Injector
To penetrate into the genital tract of the female, the male organ should be stiffened on request. The solution for the human penis pendulus is to use the arterial blood flow injected into an extensible structure: the two corpora cavernosa that has an internal mesh wired cavity and below, the urethra [4] (Fig. 10.1).
Fig. 10.1
Dissection of the anterior perineum in man. (a) Seen from the front: 1. Cavernous body of the penis; 2. Urethra; 3. Bulbospongious muscle; 4. Ischiocavernous muscle; 5. Centrum tendineum perinei. (b) After resection of cavernous bodies: 1. Inferior branch of pubis; 2. Dorsal vein of penis; 3. Penetration of the cavernous artery into the cavernous bodies; 4. Section of cavernous body; 5. Pillar of the cavernous body
But hydraulics has precise principles and stiffness of the penis can be obtained only by increasing the input flow and reducing the output flow. This is the classical problem of filling a bathtub that can be done by opening the taps and closing the outlet; otherwise the tub is half full.
A great deal of research was needed to understand precisely the mechanism of erection [5, 6]. In 1900 an Austrian histologist Viktor von Ebner (1842–1925) described pads on the wall of the cavernous arteries penetrating within the corpora cavernosa able to dilate the arteries to fill them up. But a French urologist G. Conti in 1952 defined active valves on the outside veins [7] responsible for blocking the venous flow and for generating erection. However the use of intracavernous injection of papaverine to create an erection as demonstrated particularly by R. Virag [8] allows to give the major role to the sinusoids which form the lattice of the corpora cavernosa very rich in smooth muscle cells. During erection they dilate by relaxation, which initiate the penile turgor [9].
The mandatory venous blocking was well explained in particular by Lue and Tanagho. The venous plexus under the tunica albuginea of the penis are compressed, and the venous return is reduced to maintain the stiffness of the erection [10].
There is in the retracted state, resulting in flaccid penis, a sympathetic activation of the smooth muscle of the cavernous walls and during erection, a collapse of them by a parasympathetic action.
At the distal end of the injector is a penile spongy glans that has its own vascular network and also its specific spinal cord centre activation [11]. It is therefore two erections: spongy with turgid glans induced by the spinal centre L1/L2 and cavernous by the spinal centre S2/S3/S4. The clinical study of paraplegic patients clarified these functional notions. These spinal erection centres are under brain control with a “conditional” command related to mental factors, which explains the frequent erection inhibitions of central origin [12]. We must also remember the importance of venous factors in erection [13] which condemns the surgical methods using an adjacent artery like epigastric artery to cover deficiency of cavernosal arteries.
10.2.2 Bulbospongiosus Urethral Pump Activating the Injector
Once introduced, the penis injector needs to propel the sperm out of the urethra which can only be done by a muscle action. This acts on the urethral spongy bulb placed below the prostatic portion of the urethra. Inside is the verumontanum, a micro-canal connected with the seminal vesicles—the storage sperm tanks—placed behind and above the prostate.
Thanks to a striated fibre layer from the striated bulbospongiosus muscle in the manner of a surrounding sleeve around the spongy bulb, a pump effect is obtained by crushing rhythmically the urethral tube. That is a similar work as peristaltic pumps used for extracorporeal circulation (Fig. 10.2). The real problem, however, is to find the solution to order this rhythmic pump during ejaculation.
